RE: WAL & SHM principles

> > Pros: upper layers can think thet buffers are always safe/logged and
> >       there is no special handling for indices; very simple/fast redo
> > Cons: can't implement undo - but in non-overwriting is not needed (?)
> 
> But needed if we want to get rid of vacuum and have savepoints.

Hmm. How do you implement savepoints ? When there is rollback to savepoint
do you use xlog to undo all changes which the particular transaction has
done ? Hmmm it seems nice ... these resords are locked by such transaction
so that it can safely undo them :-)
Am I right ?

But how can you use xlog to get rid of vacuum ? Do you treat all delete
log records as candidates for free space ?

regards, devik